Touch Panel, and Touch-Type Input Apparatus and Control Method Therefor

ABSTRACT

A touch panel capable of detecting a pen and a finger, capable of corresponding to multi-touch, capable of detecting pressing force, and capable of reducing the use amount of a transparent electrode as much as possible. The touch panel has a piezoelectric sheet of poly-L-lactic acid having a predetermined stretching axial direction, electrodes that are opposed to each other and formed on the piezoelectric sheet do not cover the entire surface of the piezoelectric sheet and are formed so that they are discretely distributed in plural positions. The piezoelectric sheet is brought into the condition that tension is imparted in directions not coincident with the stretching axial direction.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of application Ser. No.13/668,487, filed Nov. 5, 2012, which is a continuation of Internationalapplication No. PCT/JP2011/059919, filed Apr. 22, 2011, which claimspriority to Japanese Patent Application No. 2010-106119, filed May 6,2010, and Japanese Patent Application No. 2010-178304, filed Aug. 9,2010, the entire contents of each of which are incorporated herein byreference.

FIELD OF THE INVENTION

The present invention relates to a touch panel, and a touch-type inputapparatus and a control method therefor, and in particular to a touchpanel containing a piezoelectric sheet, and a touch-type input apparatusconfigured by using the same, and a control method therefor.

BACKGROUND OF THE INVENTION

In recent years, input devices employing a so-called touch panel system,namely touch-type input devices have greatly increased. Not only forautomatic teller machines (ATM) at banks and ticket-vending machines atstations, but also for portable phones, portable game machines andportable music players, the touch panel system has been increasinglyemployed as an input interface in association with the development inthe thin display art.

A majority of touch panels that are currently used are based on theresistance film system or the electrical capacitance system, and besidesthese, those based on the optical system, electromagnetic inductionsystem, and those utilizing surface acoustic waves by piezoelectricityare known. Usually, positional information is detected by means of thesesystems. To be more specific, the position where the operator touches(presses) on the touch panel is acquired as coordinate information, anda specified process is executed based on this information. Asrepresented by a bank ATM, an operator of the device is able to operateit as if he/she pressed an actual button by touching the part of abutton displayed on the screen. As a result of recent development ingraphic user interface (GUI) processing technique, there is also known adevice that enables a user to scroll the displayed image by stroking thescreen, or to directly control a graphically-displayed slide switch witha finger.

In terminal information devices represented by “iPhone (registered tradename)”, a so-called multi-touch system in which an operation is madewith two fingers is becoming mainstream in recent years. In the time tocome, further diversity will be required for touch panels, and in recentyears, the request to obtain information of pressing force concurrentlywith positional information is increased. To be more specific, if twokinds of information regarding what position on the screen is touched bythe operator with what strength can be detected, the operability will befurther improved.

As an art regarding this, Japanese Patent Laying-Open No. 5-61592(Patent Literature 1) discloses the technique of concurrently detectingpositional information and pressing force information by overlapping aposition detecting device and a pressure-sensitive sensor.

Japanese Patent Laying-Open No. 2006-163618 (Patent Literature 2)discloses a system of acquiring pressing force information using apiezoelectric sheet while acquiring positional information by detectingat what part the detected voltage appears in plural electrode wiresformed in a grid form in the piezoelectric sheet.

However, in the touch panel described in Patent Literature 1, on theordinary touch panel that detects only position, a pressure-sensitivesensor formed from a piezoelectric sheet or a pressure-sensitiveresistor sheet is overlapped. This pressure-sensitive sensor covers theentire surface of the touch panel.

An ordinary touch panel is usually installed on some image displaydevice, and is requested to have high transparency. Each of the positiondetecting touch panel and the pressure-sensitive sensor has a pluralityof films and electrode layers. With this system, it is impossible todetect multi touches. Although the entirety can be made transparent bymaking the films transparent and using a transparent conductive materialsuch as indium tin oxide (ITO) for the electrode layers, there is stilla problem that the light transmittance is impaired because of the largenumber of stacked layers. Further, necessity of a large number of partsand processes leads a cost rise. Further, since the positionalinformation and the pressing force information are separately detected,there is a problem that the signal processing is complicated.

On the other hand, in the touch panel described in Patent Literature 2,the piezoelectric sheet is formed with a micro-wired electrode in a gridform for the purpose of concurrently detecting positional informationand pressing force information. Since the positional information isobtained based on from what electrode in the grid electrode the signalis strongly detected, it is necessary to connect all of thesemicro-wires to an operation processing unit, and there is a problem thatthe structure is considerably complicated.

Japanese Patent Laying-Open No. 2006-39667 (Patent Literature 3)describes the art that enables multi-touch in a resistant film-typetouch panel.

In any of those described in Patent Literatures 1 to 3, a transparentelectrode of ITO or the like is used. ITO contains indium which is raremetal, and is susceptible to price increase due to depletion. Althoughtransparent electrodes made of materials other than ITO are known, itrequires a lot of work for providing the entire resin film with anelectrode, and some deterioration in transparency is caused becausetransmittance is not 100% even with a transparent electrode.

Generally, with a mere resistant film type touch panel, not onlymulti-touch cannot be detected, but also pressing force cannot bedetected. It also has such a problem that a transparent electrode ofwide area should be used.

Generally, with a mere electrostatic type touch panel, althoughmulti-touch is enabled, a touch with a pen cannot be applied andpressing force cannot be detected. Further, it has a problem that atransparent electrode of wide area should be used.

PTL 1: Japanese Patent Laying-Open No. 5-61592

PTL 2: Japanese Patent Laying-Open No. 2006-163618

PTL 3: Japanese Patent Laying-Open No. 2006-39667

SUMMARY OF THE INVENTION

In light of the above, it is an object of the present invention toprovide a touch panel capable of solving the aforementioned problem,capable of detecting both a pen and a finger, capable of correspondingto multi-touch, and capable of detecting pressing force, and reducingthe use amount of a transparent electrode as much as possible, and atouch-type input apparatus containing the same, and a method forcontrolling the same.

The present invention is first directed to a touch panel including apiezoelectric sheet formed of poly-L-lactic acid having a stretchingaxis oriented in a predetermined direction; and first and secondelectrodes that are opposed to each other, formed on first and secondmain surfaces opposed to each other of the piezoelectric sheet, and forsolving the aforementioned technical problem, a plurality of sets of thefirst and second electrodes are formed so that they do not cover theentire surface of the piezoelectric sheet and they are distributeddiscretely in plural positions.

The present invention is also directed to a touch-type input apparatusincluding the aforementioned touch panel, adapted to calculate aposition where a pressing operation is made and pressing force bycomparing voltages generated in each set of the electrodes when thepressing operation is made on the touch panel.

The touch-type input apparatus according to the present inventionfurther includes storage means for preliminary storing the voltages thatare obtained through a step of setting grid matrix coordinates on anoperation surface of the touch panel and a step of measuring voltagesgenerated in each set of the electrodes in association with a pressingoperation by predetermined weight application on each grid point of thegrid matrix coordinates, as base voltages in the respective grid points.

Further, the touch-type input apparatus according to the presentinvention includes:

means for determining an actual measured voltage generated in each setof the electrodes in association with a pressing operation made on theoperation surface of the touch panel by an operator;

means for calculating a ratio of the measured voltage relative to thebase voltage for each set of the electrodes for each of the grid points;

means for determining an average of the ratio for each set of theelectrodes for each of the grid points;

means for determining a standard deviation of the ratio for each of thegrid points;

means for ranking the grid points in ascending order of the standarddeviation;

means for selecting predetermined top n grid points in the ranked gridpoints;

means for determining a coordinate (X, Y) of a pressing position atwhich a pressing operation is made by an operator as

X=Σ(Xk/Sk)/Σ(1/Sk), Y=Σ(Yk/Sk)/Σ(1/Sk)

when the coordinate of the selected grid point is represented by (Xk,Yk) (k=1, 2, . . . , n), and the standard deviation is represented by Sk(k=1, 2, . . . , n); and

means for determining pressing force of a pressing operation made by anoperator by multiplying the applied weight by the ratio of the top gridpoint in the ranking.

The present invention is also directed to a method for controlling atouch-type input apparatus including the aforementioned touch panel,adapted to calculate a position where a pressing operation is made andpressing force by comparing voltages generated in each set of theelectrodes when the pressing operation is made on the touch panel. Themethod for controlling a touch-type input apparatus according to thepresent invention first includes:

a first preliminary step of setting grid matrix coordinates on anoperation surface of the touch panel;

a second preliminary step of measuring voltages generated in each set ofthe electrodes in association with a pressing operation by predeterminedweight application on each grid point of the grid matrix coordinates;and

a third preliminary step of storing the voltages obtained by the secondpreliminary step in a memory as base voltages in the respective gridpoints.

Further, in an actual use, the method includes:

a first practical step of determining an actual measured voltagegenerated in each set of the electrodes in association with a pressingoperation made on the operation surface of the touch panel by anoperator;

a second practical step of calculating a ratio of the measured voltagerelative to the base voltage for each set of the electrodes for each ofthe grid points;

a third practical step of determining an average of the ratio for eachset of the electrodes for each of the grid points;

a fourth practical step of determining a standard deviation of the ratiofor each of the grid points;

a fifth practical step of ranking the grid points in ascending order ofthe standard deviation;

a sixth practical step of selecting predetermined top n grid points inthe ranked grid points;

a seventh practical step of determining a coordinate (X, Y) of apressing position at which a pressing operation is made by an operatoras

X=Σ(Xk/Sk)/Σ(1/Sk), Y=Σ(Yk/Sk)/Σ(1/Sk)

when the coordinate of the selected grid point is represented by (Xk,Yk) (k=1, 2, . . . , n), and the standard deviation is represented by Sk(k=1, 2, . . . , n); and

an eighth practical step of determining pressing force of a pressingoperation made by an operator by multiplying the applied weight by theratio of the top grid point in the ranking.

In the aforementioned second preliminary step and first practical step,a voltage generated in each electrode may be detected at the time ofoperation in a pressing direction (the direction approaching theoperation surface) or at the time of operation in a reverse pressingdirection (the direction leaving from the operation surface) in pressingoperation made on the operation surface of the touch panel.

According to the touch panel of the present invention, it is possible todetect an operation made with a pen or a finger, and to correspond tomulti-touch, and further to detect pressing force. Since the electrodeis not formed to cover the entire surface of the piezoelectric sheet, itis not necessary to use a large amount of material for a costlytransparent electrode. Further, since electrodes are discretely formedso that they are distributed in plural positions, it is possible toimprove the light transmissivity of the touch panel by devising thepositions of the electrodes.

For example, since an electrode situated in an outer circumferentialpart of the piezoelectric sheet is not particularly necessary to havetransparency, metal such as aluminum, copper, gold or nickel that isinexpensive compared with a transparent electrode material may be usedas an electrode material. In other words, only for the electrode formedat the position blocking the sight toward the display surface, the onebased on indium tin oxide, indium oxide.zinc oxide, zinc oxide orpolythiophene, which is a transparent electrode material may be used asneeded.

In the touch panel according to the present invention, when thepiezoelectric sheet is brought into the condition that tension isimparted in a direction not coincident with the direction of stretchingaxis, the detection sensitivity, particularly the detection sensitivityfor multi-touch can be drastically improved.

In the foregoing case, when the piezoelectric sheet is bonded togetherwith the surface protection film with a curable adhesive in a regionextending in a direction not coincident with the stretching axis, and isbonded together with the surface protection film with a non-curableadhesive in the remaining region, it is possible to impart tensioneasily and stably in a predetermined direction of the piezoelectricsheet.

According to the touch-type input apparatus of the present invention andthe method for controlling the same, even when the number of electrodesdistributed on the piezoelectric sheet is relatively small, it ispossible to acquire positional information for discrete positions,namely any position in the entire surface based on discrete base datasuch as base voltages that are preliminary determined, and toconcurrently detect pressing force.

In the second preliminary step and the first practical step in themethod for controlling a touch-type input apparatus according to thepresent invention, by determining whether the voltage generated in eachset of the electrodes is detected at the time of operation in a pressingdirection or at the time of operation in a reverse pressing direction inpressing operation made on the operation surface of the touch panel,based on polarity of the voltage having the largest absolute value amongvoltages generated in each set of the electrodes, it is possible to makedetermination more reliably.

By not using the base voltage in the electrode showing a voltage valuesmaller than a predetermined threshold among the base voltages, in thesecond practical step in the method for controlling a touch-type inputapparatus according to the present invention, it is possible to increasethe reliability of processing, and to reduce the load on the processingcapacity.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1(A) and 1(B) show a touch panel 1 contained in a touch-type inputapparatus according to the first embodiment of the present invention,and FIG. 1(A) is a plan view and FIG. 1(B) is a section view along theline B-B in FIG. 1(A).

FIG. 2 is a view for illustrating piezoelectricity of PLLA.

FIGS. 3(A) and 3(B) are views comparatively showing voltages generatedbetween each of electrodes 21 a to 24 a and each of electrodes 21 b to24 b when a predetermined point in touch panel 1 shown in FIGS. 1(A) and1(B) is pressed, and FIG. 3(A) represents pressed points, and FIG. 3(B)represents the voltages generated in correspondence with the pointsshown in FIG. 3(B).

FIG. 4 is a view corresponding to FIG. 1(A), showing a touch panel 1 aaccording to the second embodiment of the present invention.

FIG. 5 is a view corresponding to FIG. 1(A), showing a touch panel 1 baccording to the third embodiment of the present invention.

FIGS. 6(A) and 6(B) show a piezoelectric sheet 3 contained in a touchpanel 1 c according to the fourth embodiment of the present invention,and FIG. 6(A) is a plan view, and FIG. 6(B) is a section view along theline B-B in FIG. 6(A).

FIG. 7 is a block diagram showing circuitry of a touch-type inputapparatus 100 having touch panel 1 shown in FIGS. 1(A) and 1(B).

FIG. 8 is a view for illustrating grid matrix coordinates set for anoperation surface of touch panel 1.

FIG. 9 is a flow chart showing a coordinate detection algorism executedby an operation unit 103 shown in FIG. 7.

FIG. 10 is a view for illustrating the image of determining thecoordinate of a pressing operation point executed by using thecoordinate detection algorism shown in FIG. 9.

FIG. 11 is a view corresponding to FIG. 1(A), showing a touch panel 1 dhaving an unsatisfactory configuration regarding multi-touchcorrespondence, which is a comparative example of the present invention.

FIG. 12 is a chart showing ratios of generated voltages when two pointsalong the diagonal line in touch panel 1 d are concurrently touched intouch panel 1 d shown in FIG. 11.

FIG. 13 is a chart corresponding to FIG. 11, showing the positions thatare pressed for obtaining the generated voltages shown in FIG. 12.

FIG. 14 is a chart showing ratios of generated voltages when two pointsare concurrently touched in touch panel 1 shown in FIG. 1.

FIG. 15 is a chart corresponding to FIG. 1(A), showing the positionsthat are pressed for obtaining the generated voltages shown in FIG. 14.

FIGS. 16(A) and 16(B) show a touch panel 1 e according to the fifthembodiment of the present invention, and FIG. 16(A) is a plan view, andFIG. 16(B) is a transverse section view of the center of the plan view.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIGS. 1(A) and 1(B) show a touch panel 1 according to the firstembodiment of the present invention, and FIG. 1(A) is a plan view andFIG. 1(B) is a section view along the line B-B in FIG. 1(A).

As shown in FIG. 1(B), touch panel 1 has such a sectional structure thata surface protection film 2, a piezoelectric sheet 3 havingpiezoelectricity, a rubber elastic body 4, and base body 5 are stackedin this order. More specifically, piezoelectric sheet 3 is bondedtogether with surface protection film 2, and rubber elastic body 4 isdisposed between surface protection film 2 and base body 5. Rubberelastic body 4 permits deformation of piezoelectric sheet 3, and isformed from an elastomer or a gel material, however, the gap betweenpiezoelectric sheet 3 and base body 5 may be left as a space.

Typically, touch panel 1 is arranged on the surface of a flat paneldisplay (FPD) such as a liquid crystal display, organic EL display,plasma display, or electronic paper. Therefore, each elementconstituting touch panel 1 is preferably formed from a material havingtransparency. In this case, base body 5 described above may be formedfrom FPD. In the following, description will be made on the assumptionthat base body 5 is formed from FPD.

Surface protection film 2 constitutes an operation surface on which apressing operation by an operator is to be made, and is formed from, forexample, a film made of polyethylene terephthalate, polyethylenenaphthalate, polycarbonate or poly propylene, or a glass plate. Althoughomitted in the drawing, surface protection film 2 may be formed on itssurface with an antireflection film or a scratch-resistant orantifouling hardcoat layer, or a composite layer thereof. FIG. 1(A) isillustrated in such a condition that surface protection film 2 isremoved.

Piezoelectric sheet 3 is formed of a uniaxially stretched poly-L-lacticacid (PLLA). In FIG. 1(A), a stretching axial direction of PLLA isrepresented by an arrow 10. PLLA has the advantage of being highlytransparent.

On a first main surface 3 a of piezoelectric sheet 3, first electrodes21 a to 25 a are formed, and on a second main surface 3 b that isopposed to first main surface 3 a of piezoelectric sheet 3, secondelectrodes 21 b to 25 b are formed so that they are opposed tocorresponding ones of first electrodes 21 a to 25 a with piezoelectricsheet 3 interposed therebetween. As to second electrodes 21 b to 25 b,only electrode 25 b is shown in FIG. 1(B).

In a section view of FIG. 1(B), the thickness of each element isexaggeratingly shown. Actually, the thickness of piezoelectric sheet 3is about 50 to 100 μm. Of course, the thickness may be larger than orless than this range considering the entire size of piezoelectric sheet3 and the piezoelectric characteristic itself of piezoelectric sheet 3.Thickness of any element is a design item to be determined depending onthe entire design.

Piezoelectric sheet 3 is fixed to a strong frame body (not illustrated)while it is constrained in the directions of arrows 11 a and 11 b. As aresult, piezoelectric sheet 3 is in such a condition that tension isimparted in the directions of arrows 11 a and 11 b.

FIG. 2 is a view for illustrating piezoelectricity of PLLA. When anelectric field in the direction represented by a symbol 32 is applied toa piezoelectric sheet 30 formed of PLLA in a square shape, deformationinto a substantially rhomboidal shape as shown in a solid line 31occurs. In FIG. 2, the deformation is shown quite exaggeratingly.

In FIG. 2, an arrow 33 represents a stretching axial direction of PLLA.Such deformation is deformation derived from piezoelectric constant d₁₄of PLLA. Briefly, piezoelectric sheet 30 elongates along the axis in thedirection that forms approximately 45 degrees with stretching axialdirection 33 (direction of diagonal line), and contracts along the axisoriented in the direction of 90 degrees from the former direction. Thisis a piezoelectric reverse effect. In reverse, when deformation asrepresented by a solid line 31 is caused to occur by external force, anelectric field in the direction represented by symbol 32 occurs, andwhen electrodes are formed on both main surfaces of piezoelectric sheet30, voltages are generated in these electrodes. This is a piezoelectriceffect. This reveals that the case that causes such rhombic deformationrealizes the piezoelectric effect most efficiently.

Again returning to FIGS. 1(A) and 1(B), in touch panel 1, sincepiezoelectric sheet 3 is constrained in the directions of arrows 11 aand 11 b, for example, when a center part of piezoelectric sheet 3 ispressed to deform, deformation as represented by solid line 31 in FIG. 2occurs in piezoelectric sheet 3.

FIGS. 3(A) and 3(B) are views comparatively showing voltages generatedbetween each of electrodes 21 a to 24 a and corresponding electrodes 21b to 24 b when a predetermined point in touch panel 1 is pressed. Thatis, the graph of FIG. 3(B) shows voltage occurring at channel 1 (CH1)between electrodes 21 a and 21 b, voltage occurring at channel 2 (CH2)between electrodes 22 a and 22 b, voltage occurring at channel 3 (CH3)between electrodes 23 a and 23 b, and voltage occurring at channel 4(CH4) between electrodes 24 a and 24 b when predetermined positions <1>,<2>, . . . , <9> in touch panel 1 shown in FIG. 3(A) are pressed. Here,center electrodes 25 a and 25 b are not used.

As shown in FIG. 3(B), the generation pattern of voltage is diverse, andit is revealed that a planar position on touch panel 1 can be recognizedby recognizing this pattern.

Here, if piezoelectric sheet 3 is made larger than base body 5, andelectrodes 21 a to 24 a situated in the outer circumferential part arecovered with a frame (not illustrated), there will be no electrodeexcept for electrode 25 a on the image displayed in base body 5.Therefore, it is not necessary to form a transparent electrode unlesselectrode 25 a is formed. That is, electrodes 21 a to 24 a andelectrodes 21 b to 24 b can be formed by vapor deposition, sputtering orplating of aluminum, copper, silver, gold and so on, and touch panel 1can be provided at a low price.

Electrodes 25 a and 25 b situated in the center are not necessary.However, by forming these electrodes 25 a and 25 b from a transparentelectrode material based on one kind selected from the group consistingof indium tin oxide, indium oxide.zinc oxide, zinc oxide andpolythiophene, and arranging them in the center of piezoelectric sheet3, the voltage generation pattern is further diverse, and the detectionresolution can be further increased.

As described above, when the mechanism that results in deformationsimilar to deformation according to the piezoelectric reverse effect ofPLLA is employed, diverse voltages can be taken out at highestefficiency. That is, the embodiment described above is the best mode.

As shown in FIG. 1(A), when it is difficult to apply tension only in thedirections of arrows 11 a and 11 b, the result similar to that of thebest mode can be obtained by applying tension to the entirepiezoelectric sheet 3 and applying stronger tension only in thedirections of arrows 11 a and 11 b.

FIG. 4 is a view corresponding to FIG. 1(A) showing a touch panel 1 aaccording to the second embodiment of the present invention. In FIG. 4,the element corresponding to the element shown in FIG. 1(A) is denotedby the same reference numeral, and overlapping description will beomitted. FIG. 4 shows a preferred electrode arrangement and preferredexamples of tension directions 11 a and 11 b when stretching axialdirection 10 is at diagonally 45 degrees.

For example, when four corners of piezoelectric sheet 3 are stretchedunder the equivalent tension and fixed, the voltage patterns fromelectrodes 21 a to 24 a resemble even for different positions where apressing operation is made, making it difficult to detect the position(see FIG. 11). On the contrary, under tension directions 11 a and 11 bas shown in FIG. 4, it is possible to obtain diverse voltage generationpatterns as shown in FIG. 3(B) as is the case with the embodiment shownin FIGS. 1(A) and 1(B), and to detect the position made more correctlyby arranging respective sides of electrodes 21 a to 24 a atapproximately the center of each side.

In FIG. 1(A) and FIG. 4, electrodes 21 a to 24 a are arranged in thesame size at symmetric positions, however, the position and the size arenot particularly limited. As to the size of electrodes 21 a to 24 a, itmay be any size insofar as sufficient voltage is obtained by anamplifier used for amplifying voltages from electrodes 21 a to 24 a. Themagnitude of voltage of each electrode may be intentionally madedifferent, and thereby the magnitude of the generated voltage may becontrolled.

The number of electrodes 21 a to 24 a formed in the outercircumferential part is not necessarily four, and it may be, forexample, three, or may be increased to six or nine. In the case where acertain threshold is predetermined, and voltages lower than thepredetermined threshold are not used, pattern recognition cannot beachieved if the number of electrodes is small, however, such a case canbe cleared if a sufficient number of electrodes are provided. By settingpositions of electrodes asymmetrically or setting sizes of electrodesasymmetrically, the voltage generation patterns as shown in FIG. 3(B)are less likely to be symmetric, and judgment is further facilitated.

Likewise, as to electrode 25 a situated in the center, the number isarbitrary, and electrode 25 a may not be provided.

FIG. 5 is a view corresponding to FIG. 1(A), showing a touch panel 1 baccording to the third embodiment of the present invention. In FIG. 5,the element corresponding to the element shown in FIG. 1(A) is denotedby the same reference numeral, and overlapping description will beomitted.

FIG. 5 shows a modified example of the electrode configuration. Morespecifically, first electrodes 41 a to 46 a are provided on first mainsurface 3 a of piezoelectric sheet 3, and electrodes 41 a to 46 a aredesigned to have different sizes, and the positions do not follow aregular rule. Although not illustrated, this also applies to secondelectrodes that are formed on the second main surface of piezoelectricsheet 3, so that they are opposed to first electrodes 41 a to 46 a.

While the tension direction is not illustrated, as the point to whichtension is imparted, the part where electrode 42 a and electrode 45 aare situated, or the part where electrode 43 a and electrode 46 a aresituated is conceivable. Of course, a similar effect can be obtained forother points than this. The tension is imparted most preferably in thedirection that forms approximately 45 degrees with stretching axialdirection 10, but may be applied in other direction, and for therectangular shape as is piezoelectric sheet 3 shown in FIG. 5, tensionis applied desirably in either one direction coinciding with thediagonal line direction.

Also the cutting direction of the film which is a material forpiezoelectric sheet 3 may be varied so that the diagonal line directionforms 45 degrees with the stretching axial direction. In other words,the stretching axial direction is made different from stretching axialdirection 10 shown in the drawing.

It is anyway desired to make the tension direction not completelycoincident with stretching axial direction 10.

The shape of the electrode is not limited to a rectangle and may haveany shape.

Some of the plural electrodes may be connected in series. This will beconcretely described below.

FIGS. 6(A) and 6(B) show piezoelectric sheet 3 contained in a touchpanel 1 c according to the fourth embodiment of the present invention,and FIG. 6(A) is a plan view, and FIG. 6(B) is a section view along theline B-B of FIG. 6(A). In FIG. 5, the element corresponding to theelement shown in FIGS. 1(A) and 1(B) is denoted by the same referencenumeral, and overlapping description will be omitted.

In FIGS. 6(A) and 6(B), a plurality of electrodes are formed along theouter circumferential part of piezoelectric sheet 3, and part of theseelectrodes are connected in series. To be more specific, as shown inFIG. 6(B), a first electrode 51 a and a second electrode 52 b aremutually connected by a connecting line 57, and a first electrode 52 aand a second electrode 53 b are mutually connected by a connecting line58, and thereby the electrodes from an electrode 51 b to an electrode 53a are serially connected. Also, a second electrode 54 b and a firstelectrode 55 a are mutually connected by a connecting line 59, and asecond electrode 55 b and a first electrode 56 a are mutually connectedby connecting line 60, and thereby electrodes from an electrode 54 a toan electrode 56 b are serially connected.

Connecting lines 61 and 62 respectively connected to second electrode 51b and first electrode 53 a, and connecting lines 63 and 64 respectivelyconnected to first electrode 54 a and second electrode 56 b areconnected to an amplifier (not illustrated). By serially connectingelectrode pairs that generate the same potential as described above, itis possible to increase the detection voltage, and to further reduce theerror with respect to noise.

Next, a method for detecting the position and the pressing force basedon the voltage generated by a pressing operation will be described.

FIG. 7 is a block diagram showing circuitry of a touch-type inputapparatus 100 including touch panel 1 shown in FIGS. 1(A) and 1(B).Touch-type input apparatus 100 has touch panel 1 and a processor 101,and processor 101 has a detection unit 102, an operation unit 103 and astorage unit 104. In the description with reference to FIG. 7, since itis not necessary to distinguish between first electrodes 21 a to 24 aand second electrodes 21 b to 24 b included in touch panel 1, these arecollectively called “electrode 21” to “electrode 24”, and the referencenumerals “21” to “24” are used in FIG. 7.

Referring to FIG. 7, voltage generated in each of electrodes 21 to 24 isfed to detection unit 102 respectively through connecting lines 105 a to105 d where the voltage is amplified. The amplified voltage is analyzedin operation unit 103, and the position and the pressing force aredetermined. Storage unit 104 stores base voltages that are preliminarilyacquired.

First, a preliminary process to be conducted prior to actual use oftouch-type input apparatus 100 will be described.

First, as a first preliminary step, as shown in FIG. 8, grid matrixcoordinates are set for the operation surface of touch panel 1. In FIG.8, depiction of electrodes 21 to 24 is omitted. The followingdescription will be made on the assumption that electrodes 25 a and 25 bsituated in the center do not exist. A grid point on the matrixcoordinates is an imaginary point, and is not depicted, for example, onthe operation surface. The number of grid points, namely, the number ofpartitions by the vertical axis and the horizontal axis is arbitrary.Fine partitioning improves the resolution, but complicates thepreliminary process and the subsequent operation processing.

The present invention provides a method capable of accurately detectingthe position even when the grid points are taken somewhat roughly. Thegrid points should be set at an interval of about 10 to 100 times theresolution that is eventually required. For example, when the requiredresolution is 0.2 mm, the grid points may be set at an interval of about2 to 20 mm. Selection of 10 times or 100 times the required resolutiondepends on the detection sensitivity of piezoelectric sheet 3. This isthe design item because it depends on the thickness, piezoelectricconstant and uniformity of piezoelectric sheet 3, and the material usedfor surface protection film 2.

Next, as a second preliminary step, predetermined pressing force isapplied on every grid point, and the voltage generated at each ofelectrodes 21 to 24 is measured.

In a piezoelectric body, since voltage is generated both at the time ofoperation in a pressing direction (the direction toward the operationsurface) and at the time of operation in a reverse pressing direction(the direction leaving from the operation surface) in pressingoperation, it is desired to acquire the voltages of both of these.Actually, measurement is conducted automatically using a robot and anautomated measuring device in cooperation with the robot. It is desiredto measure a plurality of times and average the measurements, or toconduct least-square approximation using data for a large number ofpoints.

Next, as a third preliminary step, the voltage obtained by theaforementioned second preliminary step is stored in storage unit 104 asa base voltage at each grid point together with the coordinate value ofthe grid point.

When n lines are set for each of the vertical direction and thehorizontal direction, the number of grid points is n×n. It is notnecessarily to make the number of division in the vertical direction beequivalent to the number of division in the horizontal direction.Further, not every division should be made at regular intervals, and thegrid intervals may be made different between the area where therequirement of resolution is high and the area where the requirement ofresolution is low.

In particular, when surface protection film 2 is formed from a glassplate, the mechanical change is larger when the center region is pressedthan when the peripheral region is pressed. Therefore, “well-varied”voltages are detected near the center, and noise is likely to occur inthe peripheral part. In association with this, the number of division inthe peripheral part is sometimes increased.

These are preliminary steps that should be conducted in advance beforetouch-type input apparatus 100 is actually used. Next, practical stepsto be executed at the time of actual use will be described.

At the time of actual use, a grid point is not necessarily touched. Theway of determining the coordinate at this time will be described. FIG. 9shows a coordinate detection algorism to be executed by operation unit103. Referring to FIG. 9, each flow will be described.

F000:

Here, the program starts.

Detection unit 102 may pull the trigger upon generation of voltage intouch panel 1 to start the program, or execution may be constantlyrepeated at a regular interval.

F001:

Operation unit 103 reads from storage unit 104 a coordinate of each gridpoint and voltages respectively generated in electrodes 21 to 24 at thetime of a reference pressing at the point.

This process is not necessarily conducted every time pressing occurs ontouch panel 1, and does not need to be executed once the data has beendownloaded onto CPU.

F002:

Measured voltages (voltage values from electrodes 21 to 24) are readfrom detection unit 102.

To detection unit 102, data about actual measured voltages generated ineach of electrodes 21 to 24 is sent in association with a pressingoperation made by an operator on the operation surface of touch panel 1.

F003:

This step is the upper end of repetitive processing.

For every grid point, the repetitive processing is executed.

F004:

A ratio of a measured voltage to a base voltage is determined for eachof electrodes 21 to 24.

One example will be shown below. The example where a measured voltageand a base voltage are compared at three grid points A, B and C isconsidered.

TABLE 1 Grid point A Electrode Measured voltage Base voltage Ratio 21 4525 1.80 22 −80 −42 1.90 23 78 36 2.17 24 37 18 2.06 Standard deviation →0.16

TABLE 2 Grid point B Electrode Measured voltage Base voltage Ratio 21 4521 2.14 22 −80 −40 2.00 23 78 41 1.90 24 37 19 1.95 Standard deviation →0.10

TABLE 3 Grid point C Electrode Measured voltage Base voltage Ratio 21 4560 .75 22 −80 −5 4.15 23 78 18 4.33 24 37 75 0.49 Standard deviation →1.76

At grid point A and grid point B shown in Table 1 and Table 2, when themeasured voltage and the base voltage are compared, a ratio of nearlytwice is observed in any electrode. On the other hand, at grid point Cshown in Table 3, the ratio of the measured voltage to the base voltageis various.

These Table 1 and Table 3 reveal that grid point C is far from theactually pressed point, and that a point near grid point A and gridpoint B is pressed. Here, the measurement error or the like is ignored.

The ratio is determined on the assumption that signs of these coincidewith each other. When signs of these do not coincide with each other,the grid point is recognized as being situated at a completely differentposition, or far apart from the pressing point, and calculation of ratiowill not be conducted.

When the base voltage or the measured voltage of a certain electrode isnear 0, there is a possibility that these have reverse signs. Foraddressing this, a threshold is preliminarily set, and when the basevoltage of a certain electrode is lower than the threshold, the data ofthat electrode will not be used in the subsequent processing.

For example, in the next step, standard deviation is typicallycalculated for four points, however, when there is a base voltage lowerthan the threshold as described above, the calculation will be conductedusing three points excluding the point that exhibits this base voltage.With such a measure, it is possible to prevent the calculated ratio frombeing extremely large when the base voltage is near 0.

F005:

Standard deviation of ratios for each electrode is determined.

Examples of standard deviation are described in Table 1 to Table 3. Asis apparent from Table 1 to Table 3, the smaller the variation in ratio,the closer to the grid point the pressing point is, and the standarddeviation is small.

A standard deviation of 0 indicates that the pressing is made just onthe grid point. Actually, the probability that the standard deviation is0 is very small in consequence of an error, however, if it is 0, thesubsequent coordinate determination processing may be interrupted andthe coordinate of the grid point itself may be determined as thecoordinate of the pressing point. In an actual program, a threshold ofstandard deviation is set, and when the standard deviation is smallerthan the threshold, the subsequent coordinate determination processingis interrupted and the coordinate of the grid point itself is determinedas the coordinate of the pressing point.

F006:

Ranking of the standard deviation obtained in the previous processing isconducted.

Owing to the respective processing, the ranking has been made in theprevious series of operations. Therefore, the rank in the previouslydetermined ranking of the currently determined standard deviation iscalculated, and the ranks of the subsequent data are shifted down.

F007:

This step is the lower end of the repetitive processing.

F003 to F007 are repeated until calculations have completed for all gridpoints.

F008:

An average value of ratios of the grid point ranked in the top rank inthe process of last F006 relative to the base voltage data isdetermined, and this is determined as a pressing force ratio.

For example, among grid points A to C shown in Table 1 to Table 3, whengrid point B is determined as the first-rank point, the average of theratios is calculated to be 1.998. Therefore, when the reference pressingforce is set at 0.10 N, the actual pressing force is determined as about0.20 N.

F009:

As shown in FIG. 9, numerical values are assigned to variables.

For making determination for the data up to the Mth rank in the ranking,the coordinate of grid point is represented by (GXk, GYk), and thestandard deviation is represented by Sk, and k=1, 2, . . . , M.Practically M of 3 or 4 is adequate. The larger number will increase theamount of calculation, and will rather increase the error.

F010:

The calculation is made as shown in FIG. 9.

The coordinate (X, Y) to be determined can be determined by thefollowing formulas:

X=Σ(GXk/Sk)/Σ(1/Sk)  (1), and

Y=Σ(GYk/Sk)/Σ(1/Sk)  (2)

(wherein, k=1, 2, . . . , M).

The image of determining the coordinate of a pressing operation point isas follows. FIG. 10 is a close-up around the higher-ranking grid pointswhen M=4. In FIG. 10, grid points 71 to 74 are depicted in the vicinityof a pressing operation point 70. On touch panel 1, such rid points donot exist in visible form.

The ranking as described above gives the first rank to grid point 74,the second rank to grid point 71, the third rank to grid point 73, andthe fourth rank to grid point 72. When respective coordinates of gridpoint 74 in first rank, grid point 71 in second rank, grid point 73 inthird rank and grid point 72 in fourth rank are (−20, 5), (−20, 10),(−25, 5) and (−25, 10), and respective standard deviations are 0.05,0.08, 0.13 and 0.18, the coordinate (X, Y) of pressing operation point70 is calculated from the foregoing formulas (1) and (2) to be (X,Y)=(−21.45, 6.97).

In the above description, the method for processing data detected at thetime of operation in the pressing direction in pressing operation hasbeen described, voltage is generated also when a finger or a pen is leftduring pressuring, namely at the time of operation in the reversepressing direction, and this voltage has reverse polarity to that at thetime of operation in the pressing direction. Focusing on the electrodewhere the largest voltage is detected, the polarity of voltage detectedin detection unit 102 is fixed. Therefore, by focusing on the polarity,it is possible to distinguish between the operation made in the pressingdirection and the operation made in the reverse pressing direction.

In an operation in the reverse pressing direction, voltages of reversepolarity are generated in all electrodes in comparison with the voltagesgenerated in a pressing operation. Therefore, by reading this polarityreversely, the data at the time of operation in the pressing directioncan be directly used.

Further, by using the data obtained at the time of operation in thereverse pressing direction in the data acquiring step, it is possible toachieve the detection with the same algorism.

Of course, it is possible to detect the position and the pressing forcebased on the data when the operation is made in the pressing direction,while no process is conducted when the operation is made in the reversepressing direction. Alternatively, the detections may be conducted onlywhen the operation is made in the reverse pressing direction while noprocess is made when the operation is made in the pressing direction.Also, the method of detecting the position only when the operation ismade in the pressing direction, and detecting the pressing force onlywhen the operation is made in the reverse pressing direction, and viceversa are possible.

Also the method of conducting full detections regardless of theoperation made in the pressing direction or in the reverse pressingdirection, and using an average of these is possible. Also, the resultat the time of in the pressing direction and the result at the time ofoperation in the reverse pressing direction may be grasped as separateresults.

Further, since the detected voltage changes by changing the pressingspeed or the releasing speed in conducting the pressing operation, thepressing operation can be made differentially in the manners of slowlypressing, quickly pressing, slowly releasing and quickly releasing, inapplication to a game machine or the like.

Next, multi-touch correspondence of the touch panel according to thepresent invention will be described.

FIG. 11 is a view corresponding to FIG. 1(A), showing touch panel 1 dhaving a defective configuration for multi-touch correspondence, whichis a comparative example of the present invention. In FIG. 11, theelement corresponding to the element shown in FIG. 1(A) is denoted bythe same reference numeral, and overlapping description will be omitted.

In touch panel 1 d shown in FIG. 11, piezoelectric sheet 3 is fixedwhile tension is applied on its four corners as shown by four arrows 11a to 11 d. Further, stretching axial direction 10 is coincident with thedirection oriented from tension direction 11 b to tension direction 11d, and electrodes 21 a to 24 a are arranged in a substantially symmetricpositional relationship near respective centers of four sides ofpiezoelectric sheet 3.

Voltages that are generated when two points along the diagonal line areconcurrently touched (multi-touched) in such touch panel 1 d are shownin the graph of FIG. 12. The graph shown in FIG. 12 is standardizedbased on the largest voltage as 1.

In FIG. 12, “CH1” represents the voltage generated at channel 1 betweenelectrodes 21 a and 21 b, “CH2” represents the voltage generated atchannel 2 between electrodes 22 a and 22 b, “CH3” represents the voltagegenerated at channel 3 between electrodes 23 a and 23 b, and “CH4”represents the voltage generated at channel 4 between electrodes 24 aand 24 b.

<1>, <2> and <3> surrounded by a circle in FIG. 12 represent thepositions where a pressing operation is made, and respectivelycorrespond to the positions <1>, <2> and <3> surrounded by a circle inFIG. 13. As can be seen from FIG. 13 where each of the positionsrepresented by <1>, <2> and <3> is found at two positions, the voltagesshown in FIG. 12 correspond to the voltages when the two positions of<1>, two positions of <2> and two positions of <3> in FIG. 13 areconcurrently pressed.

As can be seen from FIG. 12, at any of the position of <1>, position of<2> and position of <3>, the ratio of voltage between CH1 to CH4exhibits a substantially same pattern. This reveals that it is verydifficult to separate the position of <1>, position of <2> and positionof <3> from each other in multi-touch.

Also in the case of touching one center point, the voltage ratio wouldbe similar to the above, and separation from one point touch isdifficult. Therefore, even with center electrode 25 a, it would bedifficult to separate as described above.

In contrast to this, touch panel 1 as shown in FIGS. 1(A) and 1(B) whichis the best mode as described above is configured, and voltages whencenter electrode 25 a is actuated as well are shown in FIG. 14. In FIG.14, “CH1” represents the voltage generated at channel 1 betweenelectrodes 21 a and 21 b, “CH2” represents the voltage generated atchannel 2 between electrodes 22 a and 22 b, “CH3” represents the voltagegenerated at channel 3 between electrodes 23 a and 23 b, “CH4”represents the voltage generated at channel 4 between electrodes 24 aand 24 b, and “CH5” represents the voltage generated at channel 4between electrodes 25 a and 25 b.

FIG. 15 shows the positions where a press operation is made forobtaining the voltages shown in FIG. 14. Specifically, <1>, <2> . . . ,<9> surrounded by a circle in FIG. 14 represent the positions where apressing operation is made, and respectively correspond to the positions<1>, <2> . . . , <9> surrounded by a circle in FIG. 15. As can be seenfrom FIG. 15 where each of the positions represented by <1>, <2>, . . ., <9> is found at two positions, the voltages shown in FIG. 14correspond to the voltages when the two positions of <1> or the like inFIG. 15 are concurrently pressed.

As shown in FIG. 14, the ratio of voltage among CH1 to CH5 when twopoints are touched completely differs at each position of <1>, <2>, . .. , <9>, demonstrating that position detection and pressing forcedetection can be conducted concurrently. This leads the presumption thatthe variation further increases when the number of electrodes increases.

FIGS. 16(A) and 16(B) show a touch panel 1 e according to the firthembodiment of the present invention, and FIG. 16(A) is a plan view, andFIG. 16(B) is a transverse section view of the center of the plan view.In FIGS. 16(A) and 16(B), the element corresponding to the element shownin FIGS. 1(A) and 1(B) are denoted by the same reference numeral, andoverlapping description will be omitted.

In touch panel 1 e shown in FIGS. 16(A) and 16(B), piezoelectric sheet 3is bonded together with surface protection film 2 that is formed, forexample, from a glass plate, and surface protection film 2 is fixed tobase body 5 with a spacer 81 interposed therebetween. In thisembodiment, the gap between piezoelectric sheet 3 and base body 5 isleft as a space rather than being filled with a rubber elastic body.

In FIG. 16(A), surface protection film 2 is depicted in such a statethat those situated under the same are seen through. In FIGS. 16(A) and16(B), illustration of electrodes is omitted.

The diagonal direction of piezoelectric sheet 3 is not coincident withstretching axial direction 10, and it is bonded with surface protectionfilm 2 with a curable adhesive 82 in the region extending in thediagonal direction, and is bonded with surface protection film 2 with anon-curable adhesive 83 in the remaining region. As curable adhesive 82and non-curable adhesive 83, those having high transparency arepreferably used. Therefore, when highly transparent curable adhesive 82and non-curable adhesive 83 are used, the adhesives themselves andboundaries thereof are not visible.

Since non-curable adhesive 83 has relatively large elasticity orplasticity, the piezoelectric sheet is able to slightly deviate fromsurface protection film 2 when surface protection film 2 deforms. On theother hand, the part bonded by curable adhesive 82 contracts withelongation and contraction of surface protection film 2. Therefore, itis possible to produce the effect similar to that obtained when tensionis applied along the diagonal line represented by arrows 11 a and 11 bin FIGS. 1(A) and 1(B).

Touch panel 1 e shown in FIGS. 16(A) and 16(B) can be further thinnedbecause touch panel 1 e does not have a rubber elastic body. By formingsurface protection film 2 from a glass plate, it is possible to obtain atouch panel that is beautiful to the eye and resistant to impact andscratch. In this case, the glass plate that forms surface protectionfilm 2 is sufficiently thinned to such a degree that permits deformationof piezoelectric sheet 3.

REFERENCE SIGNS LIST

-   -   1, 1 a, 1 b, 1 c, 1 e touch panel    -   2 surface protection film    -   3, 30 piezoelectric sheet    -   3 a, 3 b main surface    -   10, 33 stretching axial direction    -   11 a, 11 b tension direction    -   21 to 25, 21 a to 25 a, 21 b to 25 b, 41 a to 46 a, 51 a to 56        a, 51 b to 56 b electrode    -   70 pressing operation point    -   71 to 74 grid point    -   82 curable adhesive    -   83 non-curable adhesive    -   100 touch-type input apparatus    -   101 processor    -   102 detection unit    -   103 operation unit    -   104 storage unit

1. A touch panel comprising: a piezoelectric sheet of poly-L-lactic acidhaving a stretching axis oriented in a predetermined direction; and aplurality of electrodes on said piezoelectric sheet; said piezoelectricsheet is in such a condition that tension is imparted in a directionthat forms approximately a 45 degree angle with said stretching axis. 2.The touch panel according to claim 1, wherein said piezoelectric sheethas a rectangle shape and said piezoelectric sheet is in such acondition that the tension is imparted in the direction which iscoincident with a direction of any one of diagonal lines of therectangle.
 3. The touch panel according to claim 2, further comprising asurface protection film; wherein said piezoelectric sheet has a firstregion extending in directions of the diagonal lines and a second regionother than the first region; the second region of said piezoelectricsheet is bonded to said surface protection film with a non-curableadhesive; the non-curable adhesive has larger elasticity than a materialbonding the first region of said piezoelectric sheet to said surfaceprotection film.